[Amps] More Capacitors vs LC filters

[John Lyles]

One more thing about big oil-filled capacitors: When the voltage gets above about 10-12 kV, manufacturers build their capacitors with series capacitor packs. Each one is wound paper or film with foil, connected by a jumper wire or strip. 
If you figure a 45 kV cap is made out of 3 series-connected 15 kV assemblies, and the total cap is, say 5 uF, then each cap must be 15 uF internally. All is fine and good until one of those packs shorts out. Lets say you are operating at 30 kV for convenience and this happens. 
Now you have two capacitors, of 15 uF each, operating at 15 kV each (approx), very close to their death zone. Doing the calculation, the original 5 uF capacitor could store up to 4 kJ at 40kV (1.3 kJ per internal cap), close as you would dare run to ratings. But is is derated to operating at 
2.25 KJ. Now, in the failure mode, which is, by the way, realistic, in a pulsed system over time,  it is operating with two assemblies and the total stored energy went up to 3.37 KJ. This is part of the problem that will cause a 4 KJ capacitor to 'rupture' and expel oil and flames, in addition to slitting metal case. 
I don't know how those big 'Lytics are made, the 3900 uF 450 VDC jobbies, but if there is are any multiple-connected caps inside, then failure scenarios like this warrant being thought about. 
John
K5PRO





> ### �with 7700 vdc no load and �24 x 3900uf caps in series, total energy is �4817 joules. �4817 joules divided by 24 caps =
> 200 joules PER cap. ���There is one heck of a big difference between a lytic with 200 joules stored in it ..vs �the 4000 joules
> stored in one of John?s big oil caps. ��The ESR �on the big 4000J oil cap is �zilch �vs the individual lytic. ��The massive 
> explosions �just don?t happen with these high C series strings of lytics. �You still have to be careful though. 
> later... Jim �VE7RF